Reflections on some Mlneralogical Systems, 385 



we can safely say that no combination has taken place between 

 these two substances, whatever may be the difficulty ex- 

 perienced in separating them. If, on the contrary, these 

 two molecules lose the form peculiar to them, as tartrate of 

 potash and tartaric acid, to effect another conjointly, we 

 should conclude that thev have combined to form but one. 

 By afterwards adding some soda as a neutralizer, we may 

 learn the true state of these principles, with respect to each 

 other, in consulting crystallotomy to know if molecules 

 of tartrate of potash and also those of tartrate of soda 

 are found, or molecules of another form, which will be 

 that of a tartrate with a double base. 



The great quantity of foreign matter which has been 

 found interposed between the physical molecules, without 

 effecting any change in their form, has shaken the faith 

 of many persons. The gres (sandstone) of Fontain- 

 bleau (quartziferous carbonated lime, Haiiy), in which the 

 law is the same as in the pure calcareous spar which 

 sometimes accompanies it, is an example. But the 

 degree of tendency to a regular form may be much greater 

 in one mineral than in another, and surmount all the 

 obstacles which the mixture of heterogeneous species 

 could oppose to it. This is what we see in our labo- 

 ratories; it is what the gres of Fontainbleau shows us 

 in that of nature. The power of becoming symmetrical 

 may vary in crystallizable substances, like the capacity of 

 saturation in salifiable bases. 



As to the octaedron considered as a primitive form, it 

 has been observed that sections by planes parallel to its 

 faces, divide it again into eight tetraedrons and six oc- 

 tacdrons, and this in succession to the ultimate point ; 

 so that, to maintain the unity of the integral molecule, 

 we must suppress in the mind one of these two figures. 

 In order to adhere to the most simple, as that which 

 appears to have the most just title to a place in nature, the 

 preference has been given to the tetraedron, in supposing 

 that between the molecules there are empty octaedral spaces. 

 Geometry has found that this hypothesis embraces one 

 third of the quantity of matter in a mineral which has 

 this primitive figure, and that the two other thirds are 

 empty. But this takes place precisely in the species of the 

 calcareous genus which has the greatest specific gravity, 

 while nothing is said of the vacuums in the other species. 

 Here, it is said, there is a contradiction. 



If we were still ignorant of all that we have learned 

 respecting the density of bodies, this objection would be 



Vol. 36. No. 151. Nov. 1810. 2 B some- 



